The subject matter disclosed herein relates generally to feed streams and, more particularly, a system for removing selenium from a feed stream.
There are several regions in the United States (e.g., the southwestern United States including New Mexico, Southern California, and parts of Texas) and throughout the world that experience shortages in potable water supplies due, in part, to the arid climate of these geographic locales. As water supplies are limited, innovative irrigation techniques for farm lands, parks, golf courses, and may be used. One method for obtaining an alternative source of potable water uses desalination systems to produce the potable water.
The desalination process may involve the removal of salts from seawater, agricultural run-off water, and/or brackish ground water brines to produce potable water. Desalination may use an assortment of filtration methods, such as nanofiltration and reverse osmosis, to separate the raw stream into a desalinated water stream and a brine stream. The brine streams may contain various salts and other materials left over after the desalination process, which may result in environmental issues associated with the disposal of the desalination brine.
One such impurity may be selenium. The EPA National Ambient Water Quality criteria adopted by most western states have a 5 part per billion (ppb) limit for protection of aquatic wildlife. In addition, field studies indicate that 2 ppb selenium may impact endangered aquatic species due to bio-accumulation in aquatic food chains. Certain selenium removal techniques use bioreactors and/or hydrometallurgical purification methods. In certain systems, filter cakes with high elemental selenium content may be disposed of. The filter cakes may re-oxidize and leach into rivers and streams over a period of time. Such systems may be unsuitable for selenium removal since the selenium can enter the aquatic food chains. In other systems, hydrometallurgical purification methods are used to produce industrial grade selenium for sale. The hydrometallurgical purification methods are large scale processes that use high heat and a large amount of energy, and produce selenium containing waste water streams. As such, hydrometallurgical purification methods may not be economically or environmentally feasible for desalination facilities. Therefore, energy-efficient and innovative selenium removal systems that remove selenium from feed streams may be beneficial.